Muwatta Malik 287
موطأ مالك#287SahihYahya related to me from Malik from Nafi from Abdullah ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, said, "Prayer in congregation is better than the prayer of a man by himself by twenty-seven degrees
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Salim al-HilaliSahih
In-book reference: 8:1